I posed that very question to S&B and their reply was "aesthetics only." They said that the Variable looked too much like competitive scopes, so they radiused the bell and the area around the zoom ring to give the newer Zenith a unique look so that at a glance, people would immediately recongnize it as "S&B". Actually, the Zenith objective bell looks similar to Pentax scopes. Look at the specs for FOV and length between a Variable and Zenith and they are identical. I've heard claims that the Zenith is slightly improved optically over the Variable, but S&B said the two scopes have exactly the same optics and internal mechanics. There is a very slight difference in weight between the two, probably just due to the tube differences. The only other difference is with the illuminated versions. The Variable is offered in both Flash Dot and illuminated reticles (the difference being a simple dot vs. the center crosshair being illuminated). The Zenith is no longer offered in IR versions, only Flash Dot. With the Flash Dot, the Dot is not a permanent part of the reticle, and disappears completely when illumination is turned off, so that you have a fine reticle center when not using illumination, not a black version of the same dot. The IR version just changes the center of the existing reticle from black to red when turned on.
I don't own either one, but was interested in the 1.5-6X42 Zenith, and was inquiring about the differences between it and the same config. Variable.
Edited by RifleDude